Efforts in the design of integrated circuits for radio frequency (RF) communication systems generally focus on improving performance, reducing cost or a combination thereof. One area of increasing interest relates to conversion of signals, such as from analog-to-digital or digital-to-analog. Both types of conversion have benefited from the development and use of delta-sigma modulation.
Delta-sigma modulation is a technique used to generate a coarse estimate of a signal using a small number of quantization levels and a very high sampling rate. Limiting a signal to a finite number of levels introduces “quantization” noise into the system. Oversampling and the use of an integrator feedback-loop in delta-sigma modulation are effective in shifting noise, including quantization noise, to out-of-band frequencies. The noise shifting properties enable efficient use of subsequent filtering stages to remove noise and produce a more precise representation of the input.
In order to achieve desired efficiency and precision in delta-sigma modulation, a conventional delta-sigma modulator often is required to operate at fast speeds, such as for wireless communications applications. For example, faster delta-sigma modulators can be fabricated using more expensive technologies, such as SiGe or InP. These semiconductor technologies, however, tend to be impracticable and/or cost inefficient in many applications due to their lower yields.
For commercial wireless applications, in particular, there is a need for a low cost approach to implement a digital-to-digital converter having a high dynamic range and desired bandwidth.